The use of polymeric film bases for carrying photographic layers is well known. In particular, photographic elements which require accurate physical characteristics use polyester film bases, such as polyethyleneterephthalate film bases, and cellulose ester film bases, such as cellulose triacetate film bases.
It is known that the formation of static electric charges on the film base is a serious problem in the production of photographic elements. While coating the light-sensitive emulsion, electric charges which accumulate on the base discharge, producing light which is recorded as an image on the light-sensitive layer. Other drawbacks which result from the accumulation of electric charges on polymeric film bases are the adherence of dust and dirt, coating defects and limitation of coating speed.
Additionally, photographic elements comprising light-sensitive layers coated onto polymeric film bases, when used in rolls or reels which are mechanically wound and unwound or in sheets which are conveyed at high speed, tend to accumulate static charges and record the light generated by the static discharges.
The static-related damages occur not only before the photographic element has been manufactured, exposed and processed, but also after processing when the photographic element including the image is used to reproduce and enlarge the image. Accordingly, it is desired to provide permanent antistatic protection which retains its effectiveness even after processing.
To overcome the adverse effects resulting from accumulation of static electrical charges, it is known to provide photographic elements with antistatic layers including electrically conductive materials which are capable of transporting charges away from areas where they are not desired. Typically, such antistatic layers contain electrically conductive substances, in particular polyelectrolytes such as the alkali metal salts of polycarboxylic acids or polysulfonic acids, or quaternary ammonium polymers, which dissipate the electrical charge by providing a surface which conducts electrons by an ionic mechanism. However, such layers are not very suitable as antistatic layers because they lose effectiveness under conditions of low relative humidity, become sticky under conditions of high relative humidity, and lose their antistatic effect after passage through processing baths.
It is known in the art that preferred antistatic materials are those that conduct electrons by a quantum mechanical mechanism rather that an ionic mechanism. This is because antistatic materials that conduct electrons by a quantum mechanical mechanism are effectively independent of humidity. They are suitable for use under conditions of low relative humidity, without losing effectiveness, and under conditions of high relative humidity, without becoming sticky. Defect semiconductor oxides and conductive polymers have been proposed as electronic conductors which operate independent of humidity. A major problem, however, with such electronic conductors is that they generally cannot be provided as thin, transparent, relatively colorless coatings by solution coating methods. The use of vanadium oxide has proved to be the one exception. That is, effective antistatic coatings of vanadium oxide can be deposited in transparent, substantially colorless thin films by coating from aqueous dispersions.
It is known to prepare an antistatic layer from an aqueous composition comprising vanadium oxide as described, for example, in FR Patent Application No. 2,277,136, BE Patent No. 839,270, U.S. Pat. No. 4,203,769 and GB Patent Application No. 2,032,405. The composition comprising the vanadium oxide may contain a binder to improve mechanical properties of an antistatic layer produced therefrom, such as cellulose derivatives, polyvinyl alcohols, polyamides, styrene and maleic anhydride copolymers, copolymer latexes of alkylacrylate, vinylidene chloride and itaconic acid. It is also known to provide such vanadium oxide antistatic layers with a protective overcoat layer that provides abrasion protection and/or enhances frictional characteristics, such as a layer of cellulosic material.
In photographic elements, the antistatic layer comprising vanadium oxide can be located on the side of the film base opposite to the image-forming layer as outermost layer, with or without a protective abrasion-resistant topcoat layer, or can be located as a subbing layer underlying a silver halide emulsion layer or an auxiliary gelatin layer. As vanadium oxide can diffuse from the antistatic layer through the overlying protective layer or gelatin layer into the processing solutions, a diminution or loss of the desired antistatic protection results.
U.S. Pat. No. 5,006,451 describes a photographic material comprising a film base having thereon an antistatic layer comprising vanadium oxide and a barrier layer which overlies the antistatic layer and is comprised of a latex polymer having hydrophilic functionality. This patent reports that said barrier layer prevents the vanadium oxide from diffusing out of the underlying antistatic layer and thereby provides permanent antistatic protection. However, the solution provided by said patent requires a two layer contruction which requires additional investment and operating cost, and has been proved by experiments that it loses antistatic protection in certain processing solutions such as color photographic processing solutions.
Accordingly, there is still the need to provide single layer antistatic layers, using vanadium oxide, which give permanent antistatic protection in all photographic processing solutions.